The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it may be described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present technology.
Strong, permanent magnets, and in particular, so-called rare-earth magnets (containing rare earth elements and commonly referred to as Nd-magnets or SmCo-magnets) are critical to modern technology. For example, cell phones and other microelectronic devices, electric vehicles, and wind generators are all dependent on strong, permanent magnets and, in at present, mainly on rare earth magnets.
Because of the relative scarcity of rare earth elements, as their name implies, and their consequent expense, significant efforts have been undertaken to identify and develop alternative materials that have similar magnetic properties to rare earth magnets but that do not employ rare earth elements. Low Temperature Phase manganese-bismuth (LTP-MnBi) is one of the very few magnetic materials that does not use rare-earth elements and is predicted to be able to compete at these highest levels of permanent magnet performance, when properly packaged in a nanocomposite, with a soft magnetic phase.
Many applications require magnets to perform at relatively high temperatures. For example, the typical operating temperature of the electric motor in a hybrid/electric vehicle today approaches 200° C. Yet all magnets will experience a loss of bulk magnetic properties, such as magnetic coercivity, at sufficiently high temperatures; the temperature at which magnetic properties fade (referred to as Curie Temperature) depends on the composition of the magnet. For this reason, electric vehicle motors are typically equipped with temperature control systems that can limit motor output if the temperature rises above a pre-determined point. Among rare earth alternative magnets, LTP-MnBi has a magnetic coercivity maximum at about 175° C. to 225° C., with the highest reported value of 267° C.
In addition, upon heating to 355° C., bulk LTP undergoes a decomposition from ferromagnetic LTP MnBi to paramagnetic “high temperature phase” (HTP) Mn1.08Bi. When the HTP is retained below 355° C. by rapid cooling, it is designated as the “quenched high temperature phase” (QTHP). QHTP has a Curie temperature of 177° C., and hence loses all the magnetic properties above 177° C.
Accordingly, it would be desirable to provide a rare earth alternative ferromagnetic material having bulk magnetic properties that are competitive with those of the rare earth magnets, and which maintains maximal bulk ferromagnetism at temperatures higher than does LTP-MnBi.